Elucidation of the role of farnesoic acid O-methyltransferase (FAMeT) in the giant freshwater prawn, Macrobrachium rosenbergii: Possible functional correlation with ecdysteroid signaling.

Farnesoic acid O-methyltransferase (FAMeT) is a key enzyme involved in catalyzing the conversion of farnesoic acid (FA) to methylfarnesoate (MF) in the mandibular organ (MO) of crustaceans. In this study, a full-length cDNA encoding a 278-amino-acid FAMeT protein (MrFAMeT) was characterized from the giant freshwater prawn, Macrobrachium rosenbergii. Bioinformatics analysis revealed a high degree of conservation of FAMeT among crustaceans and a close phylogenetic relationship between MrFAMeT and that of Scylla paramamosain. The prokaryotic expressed MrFAMeT could catalyze the conversion of FA to MF in a radiochemical assay. Expression analysis by quantitative real time reverse transcription polymerase chain reaction (qRT-PCR) demonstrated that MrFAMeT mRNA was highly expressed in the muscle and the hepatopancreas of both females and males. During the molt cycle and the ovarian development, the mRNA expressions of MrFAMeT displayed stage-specific patterns in the muscle of both sexes and the female hepatopancreas, and the highest expressions were detected at intermolt and ovarian development stage V. Double stranded RNA (dsRNA)-mediated RNA interference (RNAi) of MrFAMeT increased expressions of myostatin in the muscle of both sexes and reduced expressions of vitellogenin (Vg) in the female hepatopancreas. Furthermore, both in the muscle and the hepatopancreas, silence of MrFAMeT downregulated the expression of ecydone receptor gene (MrEcR) and silence of MrEcR decreased the expression of MrFAMeT as well. Results in our study indicate that MrFAMeT is involved in prawn muscle growth and female vitellogenin biosynthesis and its function may be closely related with the ecdysteroid signaling.